The use of many mechanical apparatuses includes the attachment of one mechanical part to another, such as e.g. when attaching the shaft of a pump or a blower to the shaft of a motor. When two rotating shafts are attached to each other it is of uttermost importance that the shafts are well aligned, so that vibrations can be avoided. Poor alignment of shafts invariably causes damage, in terms of wrecked bearings, shaft fatigue, gasket leakage etc., and also gives rise to high power consumption.
A method often used in shaft alignment is commonly referred to as the reverse indicator method, in which a light source and a light sensor are mounted on each shaft, the light sensor on one shaft detecting light emitted from the light source on the other shaft. This technique is well known in the art and is described e.g. in U.S. Pat. No. 4,518,855.